When negotiating a curve with a typical automotive type of vehicle, the resulting centrifugal forces acting on the vehicle tend to roll the vehicle body and associated chassis (hereinafter jointly referred to as "body") about its "roll center" relative to the underlying suspension system, and also tend to displace the body and suspension system laterally outwardly tending to cause the vehicle to pivot about its outer wheels. This latter tendency is commonly known in the art as the "jacking effect." The location of the roll center is a function of the construction of the body and the configuration of the vehicle suspension system. In a conventional vehicle, the center of gravity of the vehicle is located above the roll center. Since the centrifugal forces act through the center of gravity of the vehicle, the magnitude of the couple intending to cause the body to roll about its roll center is a function of the magnitude of the centrifugal force and the vertical distance separating the center of gravity from the roll center. This vertical distance is commonly known as the "roll couple."
As the body rolls outwardly about is roll center, it tends to compress the outer suspension springs (relative to the center of the corner about which the vehicle is traveling) thus increasing the weight on the outer wheels while simultaneously unloading the inward suspension springs thereby reducing the weight on the inside wheels. As a result, the cornering traction of the vehicle is reduced.
The lateral force tending to cause the vehicle to pivot about its outer wheels, i.e. "jacking effect," acts through the portion of the vehicle known as the "reaction center." In a conventional vehicle, the reaction center coincides with the roll center. As a result, the magnitude of the jacking effect is a function of the magnitude of the centrifugal force and the elevation of the reaction center (roll center) above the ground. The height of the reaction center above the ground is commonly known as the "jacking couple."
In conventional vehicles, attempts have been made to locate the reaction center as low as possible, thereby minimizing the jacking effect. Placement of the reaction center at a low elevation, however, results in the center of gravity of the body being located at a substantial distance above the roll center thereby increasing the magnitude of the roll couple and, thus, the amount of body roll. It is to be appreciated that in a typical suspension system, the body roll and jacking effect are cumulative, both reducing the cornering ability of the vehicle.
The lateral forces generated during cornering also cause the vehicle passengers to slide sideways in their seats making it uncomfortable for the passengers. Moreover, the roll of the body during cornering is transmitted through the suspension system and changes the camber of the wheels, causing the wheels to tilt outwardly relative to the center of the corner about which the vehicle is traveling. As is well known in the art, this outward tilt of the wheels produces a side thrust ("camber thrust") tending to force the wheels in the same direction as the wheels are tilted, i.e., outwardly. As a result, tire traction is reduced.
In the past, attempts have been made to counteract the negative effects on the vehicle body suspension system and tires caused by lateral forces imposed on the vehicle during cornering. For instance, vehicles have been designed, in theory, to cause the vehicle body to tilt inwardly during cornering. In one such type of vehicle, the body is tilted with a linkage system powered by an electric motor. The motor is selectively actuated by the driver. The impracticality and inconvenience of this type of system, such as disclosed by U.S. Pat. No. 2,152,938, is clear.
In another type of vehicle, the wheels and body are tilted into a curve by a hydraulic system employing various pumps, valves, relays, reservoirs and other associated components. The operation of the hydraulic system is controlled by a valve that is actuated by the steering shaft of the vehicle. This type of hydraulic system, as disclosed in U.S. Pat. No. 2,787,473, significantly increases the complication and cost of the vehicle suspension system.
Further attempts have been made to counteract the negative effects caused by the cornering forces on vehicles by designing the suspension system so that the roll center of the vehicle body is disposed above its center of gravity. As a result, the lateral forces acting through the center of gravity tend to tilt the body about its roll center inwardly into the curve. Examples of such systems are disclosed by U.S. Pat. Nos. 2,689,747; 2,791,440; 3,150,882; and 3,598,385. These types of suspension systems typically suffer from one or more negative features, such as being far too complicated for mass production of passenger vehicles. Also, in these types of suspension systems the outside springs are highly loaded while the inside springs are relatively unloaded during cornering, thus, counteracting the gain in cornering ability achieved by tilting the body inwardly about its roll center. In addition, in designing the vehicle so that the roll center is located above the center of gravity, the elevation of the reaction center typically must be raised upwardly relative to the ground to such an extent that a high jacking effect results. This also counteracts the gain in cornering ability achieved by the inward tilting of the vehicle body. Another common drawback of these types of suspension systems is that the weight of the vehicle must be carried by the components of the suspension system that are utilized to cause the body to tilt inwardly when cornering, thereby requiring that these components be designed large enough to safely accommodate such loads. This can substantially increase the weight of the vehicle.
Accordingly, it is a principle object of the present invention to provide a vehicle in which the roll couple and the jacking couple oppose each other thereby causing the body roll to counteract the jacking effect, thus improving the cornering traction of the vehicle.
It is a particular object of the present invention to provide a suspension system for a vehicle in which the body rolls toward the inside of the corner when turning, while simultaneously increasing the downward load on the inside wheels without increasing the jacking effect imposed on the vehicle.
It is also a particular object of the present invention to provide a vehicle suspension system in which the reaction center is separate from and located at an elevation below the roll center.
It is a further object of the present invention to provide a vehicle suspension system in which the antiroll bar or other similar devices employed to control the roll of the vehicle body does not effect the function of the road springs of the vehicle.
It is another object of the present invention to provide a suspension system for a vehicle that counteracts the lateral forces imposed on the vehicle while cornering and that also is of sufficiently uncomplicated and inexpensive construction to enable the suspension system to be employed on modern, mass-produced vehicles.
An additional object of the present invention is to provide a vehicle suspension system in which the camber of the wheels is selectively controlled so that it can be varied during cornering.